The storage and thermal stability of blends of the ether-soluble fraction of bio-oil (ES) and bio-diesel are reported. Fuel properties such as viscosity, water content, acid number and average molecular weight of the ES/bio-diesel blends were measured before and after aging. Compared to the aging properties of bio-oil alone, very small changes in water content and viscosity were shown for the blends aged at 80 degrees C for 180 h. Chemical changes were characterized using gel permeation chromatography, showing a slight increase in the molecular weight over time. Further confirmation of the changes was provided through Fourier transform infrared spectrometry, thermal decomposition analysis using a thermogravimetric analyzer, proton assignment using proton nuclear magnetic resonance, and carbon assignment using carbon nuclear magnetic resonance. Overall, the study indicates that ES/bio-diesel blends are stable as fuel under the conditions tested in this paper.